This invention relates generally to electronic systems, and specifically to spacing techniques for electronic circuit components. In particular, the invention concerns an intrinsically safe compliant circuit element spacing system, which is applicable to general-purpose electronics devices including field devices and transmitters for industrial process control and monitoring applications.
Field devices include a broad range of process management devices designed to measure and control fluid parameters such as pressure, temperature and flow rate. Field devices have broad utility in manufacturing, food and beverage processing, environmental control, hydrocarbon processing and other areas, spanning a wide range of process materials including air, water, edibles and potables, bulk materials, liquid and gaseous fuels, glues, resins, thin films, and thermoplastics such as PVC (polyvinyl chloride) and polyethylene.
In general, field devices include transmitters, which are configured to measure or sense a process parameter with a sensor module, and controllers, which are configured to modify or control such a parameter with a control module (for example, by positioning a valve or regulating a pressure). Field devices also include multi-sensor transmitters such as pressure/temperature transmitters, and integrated controllers comprising both sensor modules and control modules (for example, integrated flow controllers or hydrostatic tank gauge systems).
The “intrinsically safe” designation is applied to field devices certified under one or more standards for operation in hazardous locations, including locations prone to explosive atmospheres. These standards include, but are not limited to, FM (Factory Mutual), CSA (Canadian Standards Association), SAA/SA (Standards Association of Australia/Standards of Australia), TIIS (Japanese Technology Institution of Industrial Safety), CENELEC (European Committee for Electrotechnical Standardization), and ATEX (Appareils destinés à être utilisés en ATmosphères EXplosibles) standards.
Intrinsically safe field devices are designed to prevent the release of sufficient electrical or thermal energy to cause ignition of a hazardous atmosphere in its most ignitable concentration. Simple devices such as switches, thermocouples, RTDs and resistors typically attain an intrinsically safe rating by imposing direct limits on voltage, current and stored energy. Non-simple devices (including transmitters, controllers and other field devices) also restrict the inductance and capacitance of individual electronic components, reduce thermal output, and utilize intrinsically safe field wiring barriers to lower internal voltages and currents.
In addition, intrinsically safe field devices also address component spacing, particularly with respect to compliant circuit elements. Intrinsically safe spacing isolates circuit elements from other active electronic components, in order to prevent sparking, resistive heating, and other potentially hazardous effects.
Typical intrinsically safe spacing methods utilize insulating or filler materials such as epoxies, epoxy-elastomer potting compounds, resistive films, resistive tapes, and solid plastic spacers. Unfortunately, these materials require additional manufacturing and assembly steps, adding cost and complexity to the end product. Moreover, different spacing materials are often required for different operating environments, and their inclusion can significantly increase the difficulty of diagnosing, accessing and repairing electronic faults. There remains a need, therefore, for low-cost component spacing techniques that are applicable to a wide range of electronic designs, and able to provide intrinsically safe spacing in a variety of different hazardous location applications.